Well if there was maybe some sort of a custom CSS implemented or a browser extension active, those could also explain that. But I am almost a 100% sure it is the cache. Even if you clear your site cache, it does not neccessarily mean, that the browser will immediately get the new content, if previously cache expiration headers were defined – then the browser will keep serving the cached content. If there is a CDN as well, it may also complicate the things, as it delays the changes even more.